What is mass?
Mass is the measure of how much matter is in an object. It generally refers to the weight of an object, though mass and weight are not the same. Weight refers to gravity’s force on a person, planet, or entity. Mass instead refers to the amount of matter (protons, neutrons, and electrons) an object is made up of. The weight will be added if you weigh an object on two planets because gravity differs between worlds. The mass would be the same because the amount of matter that something is made of wouldn’t change, or at least not in the same way weight would. Mass can vary due to ‘mass loss,’ caused by the atmospheric escape of gases.
Planetary mass is the term we use when measuring the mass of a planet or planet-like astronomical object. We have a specific way of measuring the mass of planets in our solar system. This is the IAU or the astronomical system of units. First, we calculate the mass of the planets in the solar system relative to the Sun. When comparing the planets in our solar system, it’s typical for the other worlds to be compared to either Earth or Jupiter. This is because earth works well for comparison as a standard terrestrial planet. In contrast, it’s easier to compare gas giants (and also exoplanets and brown dwarfs) to Jupiter instead, as Jupiter is a gas giant planet.
Did you know? Mass is usually measured in kilograms.
The mass of the Earth
The mass of the Earth is approximately 5.9722 x 1024 kg. Earth mass is used as a standard measurement in astronomy and is represented by the symbols in the image below:
The mass of the Earth is mostly made up of iron and oxygen. These represent about 32% of the Earth’s mass each. Magnesium and silicon make up another 15% each, then calcium, aluminum, and nickel account for about 1.5% each.
Measuring the mass of the Earth precisely is very difficult. It is equivalent to measuring the gravitational constant; the fundamental physical constant is known with the least accuracy.
A fundamental physical constant is a quantity believed to be universal and has a constant value in time. For example, two of the most recognizable physical constants are the speed of light (c) and the gravitational constant (G).
The mass of the Earth was first measured with any degree of accuracy in the Schiehallion experiment. This experiment took place in the 1770s and was within about 20% of the modern ‘correct’ value.
The mass of planets in the solar system (1024kg)
- The mass of Earth is 5.9722
- The mass of Mercury is 0.330
- The mass of Venus is 4.87
- The mass of Mars is 0.642
- The mass of Jupiter is 1898
- The mass of Saturn is 568
- The mass of Uranus is 86.8
- The mass of Neptune is 102
